The present application claims priority to Australian Provisional Patent Application No. PQ 8179, filed Jun. 16, 2000.
The present invention relates to dental implants, and more particularly, to an abutment used to secure a dental prosthesis to an implant fixture.
A dental implant assembly is a device that is surgically attached to a patient""s jawbone to replace one or more missing teeth. A typical dental implant includes an implant fixture that an oral surgeon inserts into the jawbone, and a prosthesis, which replaces the crown portion of a missing tooth. Currently, the most prevalent type of dental implant fixture is a root-form implant. As its name suggests, the root-form implant has an elongated shape reminiscent of the root portion of a tooth. Much like roots of natural teeth, the root-form implant penetrates the gum and anchors the prosthesis to the jawbone.
The dental implant assembly also includes an abutment, which provides an interface or transition between the implant fixture and the prosthesis. Conventional abutments typically include a substantially axisymmetric base portion, which fits into a hole formed in the implant fixture, and a conical neck portion, which projects outward from the base portion of the abutment. Besides securing the prosthesis to the implant fixture, the abutment also compensatesxe2x80x94with varying successxe2x80x94for any misalignment between the prosthesis and adjacent teeth. Misalignment can arise, for example, when the implant fixture has an orientation with respect to the gum surface that is substantially different than the adjacent teeth.
Implant assemblies employ angled abutments, as opposed to straight abutments, to account for any misalignment. Straight and angled abutments have neck portions that project outward from their base portions in directions that are, respectively, substantially parallel or non-parallel to the symmetry axes of their corresponding base portions. Therefore, if the direction or orientation of the neck portion of the abutment is represented by a longitudinal axis that intersects the symmetry axis of the base portion (or implant fixture), the resulting orientation angle is about zero for straight abutments. In contrast, an angled abutment exhibits a non-zero orientation angle. For a discussion of straight and angled abutments, see U.S. Pat. No. 5,947,733 issued to Franz Sutter et al., which is herein incorporated by reference in its entirety for all purposes.
Though widely accepted by dental practitioners, dental implants generally, and root-form implants in particular, are not without problems. For example, the neck portions of commercially available angled abutments have fixed angular displacements with respect to their base portions, which limits their usefulness. Once a patient has been fitted with an implant fixture, the dental practitioner must order an abutment having the requisite orientation angle to ensure proper alignment of the prosthesis. However, since only discrete orientation angles are available, it is often necessary to modify the abutment to achieve the requisite angular orientation, which can be a labor intensive and costly process. In some cases the necessary orientation angle may be significantly greater than what is commercially available, making it difficult to attain acceptable alignment of the prosthesis.
Dental implants having adjustable orientation angles are known, but none appear to have achieved widespread use because of design deficiencies. See, for example, U.S. Pat. No. 5,890,902 issued to Sapian; U.S. Pat. No. 5,662,475 issued to Mena; U.S. Pat. No. 5,599,185 issued to Greenburg; U.S. Pat. No. 5,302,125 issued to Kownacki et al.; U.S. Pat. No. 4,793,808 issued to Kirsch; and U.S. Pat. No. 4,832,601 issued to Linden, which are herein incorporated by reference in their entirety for all purposes. Most of the disclosed implants are limited to modest orientation angles of about twenty-five degrees or less, and many do not readily permit removal of the prosthesis following installation. Some of the disclosed implants also fail to provide a smooth transition between the prosthesis and the implant fixture, which results in poor soft tissue adaptation. To ensure accurate alignment of the prosthesis with adjacent teeth, current practice provides for fabricating an abutment and prosthesis from a cast of the patient""s mouth following insertion of the implant fixture. Some of the disclosed designs, however, do not include a mechanism for attaching the prosthesis to the abutment prior to installation, and therefore cannot take advantage of using a laboratory cast, if desired.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems described above.
The present invention provides a dental implant abutment incorporating a ball-and-socket joint, which can be constructed from standard elements to reduce costs. The abutment allows one to adjust the orientation angle of an attached prosthesis over a continuous and wide range of values (fifty degrees or more) before fixing the desired angular orientation. The abutment readily permits removal of the prosthesis following installation and provides a smooth transition between the prosthesis and the implant fixture, which results in good soft tissue adaptation. The claimed invention also allows for accurate transfer of the abutment from the laboratory cast to the jawbone.
Thus, one aspect of the present invention provides an assembly for securing a permanent prosthesis to a root-form implant fixture. The implant fixture has a head portion, an adjoining root portion, and a hole extending from the head portion into the root portion of the implant fixture. The claimed assembly includes an abutment, which comprises a base and an attachable coping. The base has a first surface that is complementary to the head portion of the implant fixture, a second surface having a shape that approximates a section of a sphere, and a third surface that defines an aperture extending between the first and second surfaces of the base. The attachable coping has an exterior surface for receiving the permanent prosthesis, first and second openings in the exterior surface, and an interior surface that defines a cavity connecting the first and second openings. A portion of the interior surface of the attachable coping that is located adjacent to the first opening in the exterior surface is shaped to slidably engage the second surface of the base so that the attachable coping can be joined to the base at a desired angular orientation.
Another aspect of the present invention provides a connector for securing the abutment to the implant fixture. The connector has a head portion and a shaft portion adjoining the head portion. The head portion of the connector has a lateral surface configured to engage the third surface of the base, and the shaft portion of the connector has external threads adapted to engage internal threads in the hole in the implant fixture. During installation, the first surface of the base of the abutment is disposed on the head portion of the implant fixture so that the respective aperture and hole of the base and the implant fixture are substantially aligned. The connector is placed in the aperture so that rotating the head of the connector using a tool inserted through the second opening in the exterior surface of the attachable coping drives the connector into the hole in the implant fixture, thereby securing the abutment to the implant fixture.